The present invention is broadly directed to the preparation of mixed organic-inorganic single phase solids from polymerizable organic compounds which are solvents for copolymerizable metal clusters having chemically bound polymerizable ligands. More specifically, this invention produces near monodisperse nanoclusters in a polymer host by cluster copolymerization with a solubilizing monomer-solvent medium. As used herein, a "metal cluster" is a molecular complex with metal-metal bonds that form triangular or larger closed structures. A metal cluster is to be distinguished from linear metal compounds of the formula M-M-M as well as from cage compounds in which metal atoms are held together by bridging ligands, typically organic. "Single phase" refers to a substantially homogeneous dispersion of dissolved portions of the metal clusters dispersed throughout a matrix of a polymerized organic solvent. The presence of a single phase may be confirmed by conventional techniques such as scanning transmission electron microscopy (STEM) and scanning electron microscope (SEM) analyses.
Substantial research efforts are being focused on the design and fabrication of organic materials containing metal clusters because of expected applications of such materials in the fields of optics and electronics. Metal clusters have displayed a variety of useful physical properties including catalysis, magnetism, and size-dependent light absorption (the quantum size effect). A major problem in the preparation of such materials is the prevention of both phase separation and aggregation of the clusters within a host matrix. Strategies attempted heretofore to control cluster aggregation, size and morphology have included electrochemical synthesis of surfactant-stabilized clusters, in situ formation of metal clusters in the polar segments of diblock copolymers, and metal vapor deposition. None of these have enabled the preparation of the products of this invention.
U.S. Pat. No. 4,297,267 (Leatherman) discloses dissolving a simple hexavalent chromium compound in a liquid diol bis(allyl carbonate) polymerizable solvent to form, after polymerization of the liquid diol, optically clear colored lenses and the like. Leatherman is limited to the use of hexavalent chromium compounds. U.S. Pat. No. 4,471,078 (Ida) discloses the preparation of selective light absorptive methacrylate resins by adding simple low molecular weight neodynium compounds (about 573 daltons) to a resin-forming methacrylic starting material and then polymerizing the methacrylic monomer. Neither patent discloses anything about metal clusters.
Solutions of metal clusters that have polymerizable organic ligands bound to the metal on the surface of the cluster also appear to polymerize and thus solidify faster than identical solutions not containing the metal clusters, since the cluster-bound monomers copolymerize with the solubilizing monomer-solvent medium to form a highly crosslinked and highly uniform matrix. Unlike simple mixtures and ordinary composites, the inorganic substance is chemically bound and thus compatibilized to the organic polymer host, providing a more uniform molecular nanocomposite. The compatibilization of the normally disparate components leads to more homogeneous optical and mechanical properties which is expected to make the products particularly beneficial for applications in nanoscale electronic, optical and mechanical devices.
Accordingly, it is an object of the present invention to prepare a solution of a polymerizable organic solvent and a metal cluster having chemically bound ligands which are copolymerizable with the organic-monomer solvent.
It is a further object to polymerize the solution to prepare a single phase solid material which contains the metal clusters homogeneously distributed throughout.